The invention relates to a control device for an electric motor having at least one phase. The present invention furthermore relates to a corresponding vehicle and a corresponding method.
Electric motors, also known as electric machines, are used today in a multiplicity of applications.
Such motors can, for example, be used in industrial plants in order, e.g., to drive various mechanical devices. Electric motors can, e.g., however also be used in vehicles in order to drive said vehicles. Such vehicles can, e.g., be electric bicycles, electric cars, hybrid vehicles or the like. Hybrid vehicles have, e.g., a conventional internal combustion engine, which is combined with an electric motor in order to reduce the fuel consumption of the vehicle or to increase the cruising range of the vehicle.
In order to actuate such electric motors, control systems are typically used which converts a DC voltage, which is provided in the vehicles, e.g., by a battery or a fuel cell, into phase voltages suitable for the actuation of the respective motor.
The German patent specification DE 10 2011 0138957 A1 discloses a conventional method for controlling an electric motor.
It is common practice today to detect the currents which flow through the individual switching elements of the control system in order to operate and to monitor the function of the control system or respectively the drive system consisting of battery, control system and electric motor. To this end, the detected current strengths are compared, e.g., with predefined maximum values and a fault is indicated if one of the detected currents lies above the corresponding maximum value.
The measured currents can also be used to control the electric motor. To this end, the individual phase currents for the phases of the electric motor or respectively the DC component of the motor current are detected during normal operation without faults.
Such an arrangement is depicted in FIG. 6. FIG. 6 shows a three-phase electric motor M, which is coupled with an inverter I. The inverter I has two switching elements for each of the three phases, which switching elements can couple the respective phase with a positive voltage + or respectively with a negative voltage −. A current sensor SE-1, SE-2, SE-3 is disposed in each of the phases, said current sensor detecting the current in the respective phase.
Sensors which lie outside of the half-bridge switch are typically used to measure the current. Hall effect sensors or sensors which use the GMR or AMR effect or something similar can, e.g., be used as sensors.
In so doing, the external sensors are relatively large, which leads to an enlargement of the required installation space and to a more complex construction. The costs are furthermore increased by the additional components.